This invention relates to a steering wheel and more particularly to a steering wheel equipped with an optical communication mechanism for allowing optical communication between the interior of the steering wheel or the steering wheel and a vehicle column.
Experiments are being conducted for providing the pad of a steering wheel with constant-speed traveling and communications apparatus switches, radio and head lamp switches, as well as a horn switch and electronic equipment such as a sound emitter and a display unit. Some of these have already been put to practical use.
A means for transmitting and receiving signals is essential to operating such electronic equipment fitted to the pad. When a steering wheel whose pad is not revolved when the steering wheel is actuated, a signal must be exchanged between the pad and column sides of a boss plate within the steering wheel. When ordinary steering wheel whoe pad is revolved is actuated, a signal must be exchanged between the steering wheel and the vehicle column.
Optical communication is one of the effective means for transmitting and receiving signals. Conventional optical communications include the following types. For a steering wheel whose pad is not revolved, at least one pair of light emitting elements and another pair of light receiving elements are installed separately opposite to one another to form more than one optical signal channel. This is necessary because one optical signal channel may be cut off. With this embodiment one optical signal channel is always usable (e.g., Japanese Patent Application (OPI) 69144/83).
for a steering wheel whose pad is revolved, a plastic photoconductive ring for conducting light from one element to another element is necessary because a light receiving (or emitting) element installed in the vehicle column is allowed to revolve on a light emitting (or receiving) element installed in the steering wheel (e.g. U.S. Pat. No. 4,456,903).
Although the prior art described above is intended to make optical communication possible at all times, the life of the parts in steering wheels used for optical communication has been not taken into consideration.
In other words, it is desired to take the life of light emitting elements into consideration when a steering wheel is put to practical use for optical communication. A light emitting diode (LED) is often employed as a light emitting element but the quantity of light to be emitted therefrom tends to attenuate gradually as time elapses.
If the quantity of light is largely attenuated because of long-term service, optical communication may be stopped and this will cause various types of equipment such as a radio, communication equipment or the like to malfunction. The quantity of light emitted from each light emitting element may attenuates to the extent that the quantity of light emitted from one of them is insufficient to maintain optical communication, provided that the light emitting element is of the type whose life is short, that it is operated under conditions detrimental to its life or that it is used for a long period of time.
Because of variations in the performance of the light emitting element, the quantity of light emitted from a particular one may quickly attenuate.